Measure of the temperature of hot energy-radiating bodies

ABSTRACT

Apparatus for determining the wavelength which corresponds to the maximum of the curve intensity of radiated energy versus wavelength of the emission received from a radiating body. For this purpose photosensible means detect a difference in the intensities of the energy received at two points disposed close to each other along the length of a spectrum of the emission of the body and these two points are displaced relatively to the length of the spectrum until this difference disappears. The maximum is then situated about midway between the points. The photosensible means may be in the form of a pair of photoelectric cells or of a single cell receiving the radiation alternately from one and the other point. The invention may be used in association with a standardized emitter to determine the importance of absorption phenomena or of the more or less &#39;&#39;&#39;&#39;black&#39;&#39;&#39;&#39; character of the body whose temperature is being measured.

[451 Jan, 161M972 [54] MIEASE @175 THE TEE U11 HUI lENElRGY-RADHATHNG@DIM [72] Inventor: lPierre lPoneet, 12 bis, Rue Trarieux, Lyon (Rhone),France [22] Filed: Sept. 23, 11969 [21] Appl. No: 060,279

Nutter; G. D., General Considerations Influencing the Design of aHigh-Accuracy lyrometer, Chapter 54 in Part I, Vol. 3 of Temperature-Its Measurement and Control in Science and Industry, American inst. ofPhysics, Reinhold, New York, 1962, p. 538, QC- 27 l- A6 Broida; H. P.,Experimental Temperature Measurements in Flames and Hot Gases, Chapter17 in Temperature Its Measurement and Control in Science and Industry.American Inst. of Physics, Vol. 2, Reinhold, New York, 1955. p. 282, QC-271-A6.

Primary Examiner-Louis R. Prince Assistant Examiner-Frederick ShoonAttorney-Alexander 8L Dowell [57] ABSTRACT Apparatus for determining thewavelength which corresponds to the maximum of the curve intensity ofradiated energy versus wavelength of the emission received from aradiating body. For this purpose photosensible means detect a differencein the intensities of the energy received at two points disposed closeto each other along the length of a spectrum of the emission of the bodyand these two points are displaced relatively to the length of thespectrum until this difference disappears. The maximum is then situatedabout midway between the points. The photosensible means may be in theform of a pair of photoelectric cells or of a single cell receiving theradiation alternately from one and the other point. The invention may beused. in association with a standardized emitter to determine theimportance of absorption phenomena or of the more or less black"character of the body whose temperature is being measured.

4 Claims, 6 Drawing lilignres PAIENIEnJAmm 3.7635 088 SHEET 1 OF 2 q. W3 9b 0 7 9 I VENTOR. PMML,

PATENIEnJmwz 3535 088 SHEET 2 UP 2 INVENTOR. 2 W L un) wwau MEAS GE THETIEMMEIRA l i .1" H Gil" ll-llUT ENERGY- htAlDllA'l'llNG BGDKIESDESCRIPTlON This invention relates to the measurement of the temperature of a hot body by relying on its radiant energy.

it is known that the total energy radiated by a hot body such as forinstance a mass of metal in a furnace or in a tundish, a refractorywall, etc. is a function of the fourth power of its temperature. inorder to determine this temperature it is therefore suflicient tomeasure the intensity of the radiated energy by means of a so-calledoptic pyrometer. Unfortunately a substantial proportion of this energyis absorbed by the more or less transparent medium situated between theradiating body and the pyrometer. Thus a quite small amount of smokerenders quite impossible any direct pyrometric measuring operation.

In the so-called bicolor method a beam of the optical energy radiated bythe body is decomposed into a spectrum by a prism or the like and theradiated energy (or more exactly its intensity) is measured at twopredetermined adjacent points along the length of this spectrum, i.e.for two predetermined adjacent wavelengths or colors. The ratio of thesetwo energies corresponds to the slope of the curve radiated energyversus wavelength in the zone comprised between the two points and thisslope is a function of the temperature. But here again absorption bysmokes or the like reduces the accuracy of the measurement. Furthermorefor a relatively large temperature variation, the variation of the slopeis relatively small and therefore the photoelectric cells, theamplifiers and like electric devices required with such a method shouldbe extremely sensitive and accurate.

it is an object of the present invention to provide a method which willbe unaffected by the presence of a noticeable amount of smoke betweenthe radiating body and the optical apparatus and which will not requirehigh-precision electronic equipment.

in accordance with the present invention a method for measuring thetemperature of an energy-radiating body consists in determining thewavelength which corresponds to the maximum of its curve intensity ofradiated energy versus wavelength.

The position of this maximum along the axis of abscissae (wavelengths)of the curve may be detected by comparing the intensities received attwo adjacent points along an optical spectrum of the radiant energyemitted by the hot body, somewhat as in the bicolor method, but while inthe latter the points are maintained at a fixed location on thespectrum, in accordance with the present application, they are displacedin unison along the said spectrum until the corresponding energiesreceived are exactly equal. When such is the case, the maximum issituated substantially midway between the two points. This operation maybe effected by means of two identical photoelecu'ic cells disposed closeto each other along the spectrum, preferably behind narrow slits, therelative displacement between the cells and the spectrum beingconveniently realized by angularly displacing the prism, grating orequivalent light-decomposing device until the responses of both cellsare equal. in a modification the spectrum is projected on a screenhaving two close parallel slits and the beams issuing from these slitsare directed in alternate succession towards a single photoelectriccell, the response of the latter being in the form of alternate pulsesof different magnitude until the maximum of the curve corresponds to thepoint of the spectrum situated substantially midway between the slits.

The knowledge of the exact temperature of the energy-- radiating bodymay further be used for determining the importance of the absorptionphenomena, or the more or less black character of the body by comparingfor the same wavelength the intensity received from the body with theintensity received from an adjustable radiating source maintained at thesame temperature.

in the accompanying drawings:

FllG. ll shows a set of curves depicting radiated energy versuswavelength for a number of temperatures.

FIG. 2 diagrammatically illustrates an apparatus according to theinvention including two photoelectric cells.

Fit]. 3 illustrates the operation of the apparatus of Fit 2.

FlGS. d and 5 show respectively in elevation and in section taken alongline V--V (FIG. d) a preferred arrangement of the cells in the apparatusof MG. 2.

FIG. 6 diagrammatically shows a modified apparatus having a singlephotoelectric cell.

FIG. 7 illustrates the response of this single cell shown in FIG. ti.

FIG. h is a diagrammatical representation of an apparatus fordetermining the importance of the absorption phenomena or forappreciating the more or less black character of the emitting body.

H6. 1 diagrammatically shows a set of curves depicting radiated energy(or intensity 1) versus wavelength corresponding to a number oftemperatures T,, T T T Each curve has a maximum situated at a wavelengthA A A A this position being uninfluenced by smoke or like usuallightabsorbing media. When the wavelength at which the maximum occurs isdetermined, the temperature of the radiating body is known with a quitesatisfactory accuracy.

Of course curves T T T T correspond to a given body, as for instance forthe theoretical black body. But most bodies (as for instance moltenmetals) behave at high temperatures almost exactly as this black bodyand it is moreover possible to use correcting coefficients in order toeliminate the small residual errors. Furthermore the curves may beplotted for any given body, if desired. it is also necessary that theabsorption of energy by the intermediate medium be unselective (i.e.,independent of the wavelength), at least in the zone of the maximum, butthis condition is generally fulfilled in the case of smoke. As to airand other gases, their absorption, while being sometimes noticeablyselective, is generally of quite small importance and does not impairthe accuracy of the maximum detecting operation.

In FIG. 2 reference numeral ll designates a substantially black body thetemperature of which (T for instance) is to be determined. A fraction orbeam of its radiated energy is received by a lens 2 which concentratesthis beam on a narrow slit 3 provided in an appropriate opaque screen.The rays issuing from this slit 3 reach an objective lens 4 which wouldnormally form at 3' an image of the slit 3 of the screen. Alightdecomposing device 5, as for instance a grating, is disposed behindlens d in such manner as to form an optical spectrum AB of the radiationof body 1. Two photoelectric cells a and 7 supported close to each otherby a carriage ll may be displaced along this spectrum AB, these cellsbeing connected with an appropriate electronic equipment (notillustrated) by means of which their responses may be compared. itcarriage is situated well beyond the point of spectrum AB whichcorresponds to the maximum of the curve T,,, the energy received bycells h and '7 will be represented by the ordinates of points such as doand 7a (lFlG. It). The electronic equipment will detect that theresponse of cell 6 is stronger than that of cell 7 (negative slope ofcurve T lfon the other hand carriage ti had been disposed on the otherside of the maximum (points 6b and 7b) the difference would have been inthe other direction (positive slope). The outlet of the electronicequipment may therefore act on an appropriate scrvornotor in order todisplace carriage til towards the left in the first case or towards theright in the second one (direction of ascending slope or of increasingintensities). Finally carriage b will stop at the position for which theresponses of both cells are of equal magnitude (points he, 70). Thepoint of spectrum AlB corresponding to the maximum of curve T, will besituated substantially midway between points dc and 7c. Thecorresponding wavelength in, is an accurate indication of thetemperature T, of body 1. The operation is unaffected by smoke or byappreciable amounts of combustion gases such as carbon dioxide. Theelectronic equipment has only to compare the responses of the cells andnot to measure these responses in a particularly accurate manner. It mayfor instance comprise a conventional differential amplifier. Thephotoelectric equipment may comprise photomultipliers, if desired.

Of course instead of displacing the cells along the spectrum, the lattercould be displaced so as to sweep across the cells, as for instance byrotating the grating 5, in which case the latter may drive a pointer ona dial to indicate directly the temperature when the equilibrium isreached between cells 6 and 7. The lenses such as 2 and 4 which inpractice absorb a large portion of infrared energy, might be replaced byspherical mirrors.

FIGS. 4 and illustrate a practical arrangement in which twophotoelectric cells such as 6 and 7 may be disposed quite close to eachother along the spectrum in order to reduce the horizontal distancebetween points 6c and 7c in FIG. 3 and thus to improve the determinationof A The spectrum AB of FIG. 2 is received on an arcuate opaque screen 9FIGS. 4 and 5 formed with two narrow slits 9a and 9b disposed at twodifferent levels (i.e., at two different positions across screen 9), butclose to each other in the horizontal (or longitudinal) direction. Thecells 6 and 7 are respectively mounted behind slits 9a and 9b and theythus receive two narrow beams corresponding to two points situatedhorizontally close to each other on curves such as T In the embodimentof FIGS. 2, 4 and 5, the photoelectric cells should be quite identicalduring their life and this condition should be frequently checked inactual practice. The apparatus diagrammatically illustrated in FIG. 6avoids this disadvantage by using a single cell. This apparatuscomprises the arcuate screen 9 with its slits 9a and 9b. The beamsissuing from these slits are deviated by mirrors, such as 11 and 12,towards spherical mirrors l3 and 14 which concentrate them towards acommon photoelectric cell 15. A rotating disk 16 is interposed betweencell and mirrors l3, 14, this disk being formed with notches orapertures which permit alternately passage of the beam from mirror 13and of the beam from mirror 14. The response of the cell 15 appearstherefore as illustrated in FIG. 7, i.e. as a succession of alternatepulses da, db of unequal height or magnitude. An appropriate electronicequipment detects the difference between da and db and acts on the prismor grating 5 so as to displace the spectrum in the proper directionalong screen 9, that is to say across slits 9a and 9b. Here again whenthe equilibrium is reached between pulses da and db, the wavelength ofthe point of the spectrum situated horizontally (or longitudinally)midway between slits 9a and 9b corresponds to the wavelength A, of FIG.3 and therefore constitutes an accurate indication of the temperature ofbody 1.

FIG. 8 illustrates how the invention may be used for the measure of theabsorption of the radiated energy by the surrounding media, or forhaving the indication of the black character, or of the color of theradiating body. The importance of absorption phenomena is of interestfor the detection of smoke. As to the color of the radiating body it mayconstitute for instance an indication of the thickness of the slag on abath of molten metal within a mould, tundish, furnace or the like.

In FIG. 8 a beam from a black radiating body 1 is received by a firstlens 2 so as to illuminate a slit 3, the rays which issue from the slitreaching an objective lens 4 with which is associated alight-decomposing device 5, here illustrated in the form of a prism. Twophotoelectric cells 6, 7 disposed close to each other along the spectrumthus realized, are connected with an electronic comparator 18. Theoutlet of the latter controls a servornotor 17 adapted to drive a shaft119 which supports prism 5.

The shaft 19 also carries another prism 20 which receives a beam from anelectric bulb 21 through an optical assembly similar to that disposedbetween body 1 and prism 5, except that the slit, here referenced 22, isadjustable in width by means of a servomotor 23 (in other words motor 23controls a slitlike diaphragm). A photoelectric cell 25 is disposed onthe spectrum formed by prism 20. Its outlet is connected with a secondcomparator 26. The outlet of comparator 26 is used for the actuation ofmotor 23.

As above explained, under the action of the comparator 18 the servomotor17 positions prism 5 so as to realize the equilibrium between theresponses of cells 6 and 7, and the angular position of shaft 19 is adirect indication of the temperature of the radiating body 1,irrespective of the importance of an absorbing mask 27 of smoke or thelike. The rheostat 24 is so adjusted that the temperature of thefilament of bulb 21 is then equal to the temperature of body 1. Thephotoelectric cell 25 is disposed in such manner as to receive the samewavelength as cell 6. The comparator 26 actuates motor 23 and thereforediaphragm 22 until cells 6 and 25 receive the same energy (it beingassumed that these cells are identical). The width of diaphragm 22 thuscorresponds to the importance of the absorbing mask 27.

In the same manner in the absence of an absorbing mask 27 (or in thepresence of a mask of known importance), if the apparatus has beenadjusted for a black body and if it is used with a gray or colored body,the variation in the width of slit 22 is an indication of the nonblack"character of the energyradiating body.

I claim:

1. An apparatus for measuring the temperature of a hot energy-radiatingbody, comprising means to form a spectrum of the energy radiated by saidbody, said spectrum having a length;

photosensible means receiving radiant energy from two distinct points ofsaid spectrum disposed close to each other along said length;

and means to displace said photosensible means along the length of saidspectrum relatively to said two points in the direction of increasingenergies until the intensities of the energies received at said twopoints are equal.

2. In an apparatus as claimed in claim I, said photosensible meansincluding two photoelectric cells respectively disposed at one and theother of said points; an opaque screen to receive said spectrum at leastin the zone thereof where said points are located, said screen beingformed with two trans verse slits disposed at said points close to eachother longitudinally of said spectrum but displaced with respect to eachother transversely of said spectrum; and each of said photoelectriccells being disposed behind one of said slits to receive radiant energyemerging therefrom.

3. In an apparatus as set forth in claim 1, said photosensible meansincluding a single photoelectric cell; and means to alternately projectonto said cell beams of radiant energy from one and the other of saidpoints, including an opaque screen to receive said spectrum at least inthe zone thereof where said points are located, said screen being formedwith two slits disposed at said points close to each otherlongitudinally of said spectrum, each for passage of a beam of radiantenergy; means embodying mirrors to receive said beams and to concentratesame towards said single cell; and screen means to alternately interruptone and the other of said beams.

4. In an apparatus as claimed in claim 1, an auxiliary source of radiantenergy;

means to vary the temperature of said source in unison with displacementof said two points along said spectnim in such manner that saidtemperature will be always equal to the temperature of said body whenthe intensities of the energy received at said two points are equal;

means to form an auxiliary spectrum of the energy radiated by saidauxiliary source;

auxiliary photosensible means disposed at a point of said spectrum;

means to displace said auxiliary spectrum relatively to saidphotosensible means along said auxiliary spectrum in unison withdisplacement of said two points along the spectrum of the energyradiated by said body in such manner that said auxiliary photosensiblemeans receive at any time an energy of the same wavelength as the energyreceived at one of said points;

and diaphragm means interposed between said auxiliary source and saidauxiliary photosensible means to permit obtaining equality between theintensities received from said auxiliary source by said auxiliaryphotosensible means and from said body at said one of said points by 5said photoaensible means receiving radiant energy from said points. i

l ii l ll n]:

1. An apparatus for measuring the temperature of a hot energyradiatingbody, comprising means to form a spectrum of the energy radiated by saidbody, said spectrum having a length; photosensible means receivingradiant energy from two distinct points of said spectrum disposed closeto each other along said length; and means to displace saidphotosensible means along the length of said spectrum relatively to saidtwo points in the direction of increasing energies until the intensitiesof the energies received at said two points are equal.
 2. In anapparatus as claimed in claim 1, said photosensible means including twophotoelectric cells respectively disposed at one and the other of saidpoints; an opaque screen to receive said spectrum at least in the zonethereof where said points are located, said screen being formed with twotransverse slits disposed at said points close to each otherlongitudinally of said spectrum but displaced with respect to each othertransversely of said spectrum; and each of said photoelectric cellsbeing disposed behind one of said slits to receive radiant energyemerging therefrom.
 3. In an apparatus as set forth in claim 1, saidphotosensible means including a single photoelectric cell; and means toalternately project onto said cell beams of radiant energy from one andthe other of said points, including an opaque screen to receive saidspectrum at least in the zone thereof where said points are located,said screen being formed with two slits disposed at said points close toeach other longitudinally of said spectrum, each for passage of a beamof radiant energy; means embodying mirrors to receive said beams and toconcentrate same towards said single cell; and screen means toalternately interrupt one and the other of said beams.
 4. In anapparatus as claimed in claim 1, an auxiliary source of radiant energy;means to vary the temperature of said source in unison with displacementof said two points along said spectrum in such manner that saidtemperature will be always equal to the temperature of said body whenthe intensities of the energy received at said two points are equal;means to form an auxiliary spectrum of the energy radiated by saidauxiliary source; auxiliary photosensible means disposed at a point ofsaid spectrum; means to displace said auxiliary spectrum relatively tosaid photosensible means along said auxiliary spectrum in unison withdisplacement of said two points along the spectrum of the energyradiated by said body in such manner that said auxiliary photosensiblemeans receive at any time an energy of the same wavelength as the energyreceived at one of said points; and diaphragm means interposed betweensaid auxiliary source and said auxiliary photosensible means to permitobtaining equality between the intensities received from said auxiliarysource by said auxiliary photosensible means and from said body at saidone of said points by said photosensible means receiving radiant energyfrom said points.